我们之前已经说明了，泌乳素诱导蛋白 (PIP) 的高表达与乳腺癌（BC）患者对标准辅助化疗（多柔比星和环磷酰胺）的反应相关，这表明该糖蛋白的缺失与肿瘤细胞对化疗的耐药性有关。因此，在本研究中，我们分析了PIP表达对BC细胞抗癌药物耐药性和BC进展的生物学作用的影响。使用实时PCR和Western blotting分析BC细胞系中的PIP和凋亡基因的表达，使用免疫组织化学检测BC组织标本中的PIP。使用体内肿瘤生长实验分析癌细胞的致瘤性。基于caspase-3活化、Annexin V结合和TUNEL检测，检测凋亡细胞。使用流式细胞术分析PIP与BC细胞的相互作用。使用两种BC细胞模型（即PPI基因敲除的T47D细胞和过表达PIP的MDA-MB-231细胞），我们发现PIP的高表达导致：(1) BC细胞对多柔比星（DOX）、4-羟基过氧化环磷酰胺（4-HC）和紫杉醇（PAX）引起的凋亡敏感性增加；(2) 在移植小鼠模型中，DOX的抗癌疗效得到改善。相应的临床研究表明，PIP表达较高的BC患者具有更长的5年总生存率和无病生存率。随后的研究显示，PIP上调下列促凋亡基因的表达：CRADD、DAPK1、FASLG、CD40和BNIP2。这种促凋亡活性是由分泌的PIP介导的，很可能涉及特定的表面受体。本研究表明，PIP高表达水平使BC细胞对抗癌药物更加敏感。化疗敏感性的增加是PIP促凋亡活性的结果，这得益于特定促凋亡基因的上调。由于PIP的高表达与患者对抗癌药物的更好反应显著相关，因此该糖蛋白可以用作辅助化疗预后评估的标记。© 2023. The Author(s).

We have previously shown that high expression of prolactin-induced protein (PIP) correlates with the response of breast cancer (BC) patients to standard adjuvant chemotherapy (doxorubicin and cyclophosphamide), which suggests that the absence of this glycoprotein is associated with resistance of tumor cells to chemotherapy. Therefore, in the present study, we analyzed the impact of PIP expression on resistance of BC cells to anti-cancer drugs and its biological role in BC progression. Expression of PIP and apoptotic genes in BC cell lines was analyzed using real-time PCR and Western blotting. PIP was detected in BC tissue specimens using immunohistochemistry. The tumorigenicity of cancer cells was analyzed by the in vivo tumor growth assay. Apoptotic cells were detected based on caspase-3 activation, Annexin V binding and TUNEL assay. The interaction of PIP with BC cells was analyzed using flow cytometry. Using two cellular models of BC (i.e. T47D cells with the knockdown of the PIP gene and MDA-MB-231 cells overexpressing PIP), we found that high expression of PIP resulted in (1) increased sensitivity of BC cells to apoptosis induced by doxorubicin (DOX), 4-hydroperoxycyclophosphamide (4-HC), and paclitaxel (PAX), and (2) improved efficacy of anti-cancer therapy with DOX in the xenograft mice model. Accordingly, a clinical study revealed that BC patients with higher PIP expression were characterized by longer 5-year overall survival and disease-free survival. Subsequent studies showed that PIP up-regulated the expression of the following pro-apoptotic genes: CRADD, DAPK1, FASLG, CD40 and BNIP2. This pro-apoptotic activity is mediated by secreted PIP and most probably involves the specific surface receptor. This study demonstrates that a high expression level of PIP sensitizes BC cells to anti-cancer drugs. Increased sensitivity to chemotherapy is the result of pro-apoptotic activity of PIP, which is evidenced by up-regulation of specific pro-apoptotic genes. As high expression of PIP significantly correlated with a better response of patients to anti-cancer drugs, this glycoprotein can be a marker for the prognostic evaluation of adjuvant chemotherapy.© 2023. The Author(s).